Light-emitting device and electronic apparatus

ABSTRACT

A light-emitting device includes: a plurality of light-emitting elements each of which has an anode, a thin organic light-emitting layer, and a cathode sequentially stacked on a substrate and emits light by excitation due to an electric field, the anode being separated from another anode by an insulating pixel partition wall; an organic buffer layer that is formed of an organic compound, covers an area larger than a region where the plurality of light-emitting elements are formed, has a step difference smaller than that of an upper surface of the cathode on the substrate, and is approximately flat; and first and second gas barrier layers that are formed of an inorganic compound, are disposed on an outer surface of the organic buffer layer, and protect the plurality of light-emitting elements against air. Only one of the first and second gas barrier layers is adjacent to an upper surface of an insulating layer formed of an inorganic compound on the substrate so as to cover an area larger than that of the organic buffer layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Application No.2005-336650, filed in Japan on Nov. 22, 2005, the entire disclosure ofwhich is hereby incorporated by reference in its entirety.

BACKGROUND

The present invention relates to a technique of sealing light-emittingelements with a thin film.

As an example of known light-emitting elements, there is an organic EL(electroluminescent) element that emits light by using a light-emittingelement having a thin organic light-emitting film composed of amulti-layered organic compound that is interposed between two electrodesand emits light by excitation due to an electric field. In a process ofmanufacturing a device having organic EL elements, in order to preventan organic light-emitting material and a cathode, which includes anelectron injection layer formed of, for example, calcium, magnesium, oraluminum complex, from deteriorating due to the presence of or contactwith air or moisture, a sealing process is performed. As examples ofknown sealing techniques, thin film sealing techniques of coveringorganic EL elements with an extremely thin inorganic compound film areknown (see, for example, JP-A-9-185994, JP-A-2001-284041,JP-A-2000-223264, and JP-A-2003-177244). In these techniques, theinorganic compound film serves as a gas barrier layer that blocks air.

In general, it is necessary to form a gas barrier layer with a largethickness in order that the gas barrier layer provides a sufficientreliability (in particular, coating reliability with respect to finecontamination that cannot be blocked even in a clean room). On the otherhand, in the thin film sealing techniques, organic EL elements areformed on a substrate and a thin gas barrier layer is formed on thesubstrate so as to cover the organic EL elements by means of a vaporgrowth method, for example. At this time, a step difference, such asunevenness, may occur on a surface of the gas barrier layer, due to thepresence of insulating pixel partition walls for separation among aplurality of elements. When the gas barrier layer having the stepdifference is formed to be uniformly thick, the stress is noticeablyconcentrated in a portion having the step difference, which causes thegas barrier layer to easily crack or be peeled off. Further, in the casewhere a gas barrier layer is a transparent and high moisture-resistanceinorganic compound layer, which is formed of, for example, a siliconcompound, the inorganic compound layer has a density and elastic modulus(Young's modulus) higher than those of an organic compound layer.Accordingly, a crack easily occurs due to the stress concentration.

If the gas barrier layer cracks or is peeled off, moisture contained inatmospheric air permeates into the organic EL elements. Accordingly, aproblem occurs in that the organic EL elements are significantlydeteriorated. Further, when the gas barrier layer is formed of anorganic compound material having a low elastic modulus in order toprevent formation of cracks or is formed to be extremely thin, it isdifficult to obtain sufficient sealing reliability even if the gasbarrier layer does not crack or is not peeled off, which also causesearly deterioration of the organic EL elements.

SUMMARY

An advantage of some aspects of the invention is that it provides alight-emitting device, in which light-emitting elements can besufficiently sealed with a gas barrier layer that is not easily crackedor peeled off, and an electronic apparatus.

According to an aspect of the invention, a light-emitting deviceincludes: a plurality of light-emitting elements each of which has ananode, a thin organic light-emitting layer, and a cathode sequentiallystacked on a substrate and emits light by excitation due to an electricfield, the anode being separated from another anode by an insulatingpixel partition wall; an organic buffer layer that is formed of anorganic compound, covers an area larger than a region where theplurality of light-emitting elements are formed, has a step differencesmaller than that of an upper surface of the cathode on the substrate,and is approximately flat; and first and second gas barrier layers thatare formed of an inorganic compound, are disposed on an outer surface ofthe organic buffer layer, and protect the plurality of light-emittingelements against air. Only one of the first and second gas barrierlayers is adjacent to an upper surface of an insulating layer formed ofan inorganic compound on the substrate so as to cover an area largerthan that of the organic buffer layer. The organic compound is acompound having a skeleton composed of carbon as a basic structure.

In the light-emitting device, since the plurality of light-emittingelements are disposed according to the insulating pixel partition wallsand the plurality of anodes interposed between the insulating pixelpartition walls, large step difference occurs on the surface of thecathode formed on the organic light-emitting layer. However, since theorganic buffer layer approximately planarizes the unevenness, such thatthe step difference at the upper surface of the organic buffer layerbecomes smaller than that at the upper surface of the cathode.Therefore, as compared with a case in which the organic buffer layer isnot provided, the gas barrier layer becomes further planarized on theplurality of light-emitting elements. As a result, the stress in the gasbarrier layer becomes low, which makes it difficult that the gas barrierlayer cracks easily.

Further, on the substrate, since the end portions of the organic bufferlayer that is approximately planarized are angled much, the gas barrierlayer located at the end portions of the organic buffer layer alsocracks easily. For this reason, since the light-emitting element regionapproximately planarized by the organic buffer layer needs to be veryreliably sealed, the first gas barrier layer and the second gas barrierlayer are provided. Specifically, the light-emitting element region iscoated with two gas barrier layers, and only end portions of the organicbuffer layer to which stress is likely to be easily applied is coatedwith only one gas barrier layer. Thus, the stress is reduced, which canprevent the crack.

Furthermore, since the organic buffer layer is formed of an organiccompound that is flexible and has low elastic modulus as compared withan inorganic compound, the stress can be easily dispersed.

As described above, according to the light-emitting device, it ispossible to reliably seal the light-emitting elements with gas barrierlayers that are not easily cracked or peeled off.

In the light-emitting device, preferably, the first gas barrier layercovers an area larger than that of the organic buffer layer, and thesecond gas barrier layer covers an area that is smaller than that of theorganic buffer layer and larger than that of the region where theplurality of light-emitting elements are formed.

According to the light-emitting device, as compared with the case inwhich the organic buffer layer is not provided, the gas barrier layerbecomes further planarized on the plurality of light-emitting elements.As a result, the gas barrier layer does not crack easily. Further, sincethe region where the plurality of light-emitting elements are formed iscoated with the first and second gas barrier layers, the gas barrierlayers are sufficiently thick, which makes it possible to reliably sealthe plurality of light-emitting elements. In addition, since the secondgas barrier layer is not provided around the end portions of the organicbuffer layer, the thickness of the gas barrier layer around the endportions of the organic buffer layer is small. Therefore, even if thegas barrier layer around the end portions of the organic buffer layer isnot flat, the gas barrier layer is not easily cracked or peeled off. Inaddition, since the organic buffer layer is formed of an organiccompound having low elastic modulus in which the stress can be easilydispersed, the crack of the gas barrier layer becomes further difficult.As described above, according to the light-emitting device, it ispossible to reliably seal the light-emitting elements with gas barrierlayers that are not easily cracked or peeled off.

Further, in the light-emitting device, preferably, the second gasbarrier layer is thicker than the first gas barrier layer.

According to the light-emitting device, since the sealing reliabilitywith respect to the plurality of light-emitting elements is not largelyaffected, it is possible to make the first gas barrier layer relativelythin. As a result, it is possible to make it difficult that the gasbarrier layers crack or are peeled off.

Furthermore, according to another aspect of the invention, alight-emitting device includes: a plurality of light-emitting elementseach of which has an anode, a thin organic light-emitting layer, and acathode sequentially stacked on a substrate and emits light byexcitation due to an electric field, the anode being separated fromanother anode by an insulating pixel partition wall; an organic bufferlayer that is formed of an organic compound, covers an area larger thanthat of a region where the plurality of light-emitting elements areformed, has a step difference smaller than a surface of the cathode onthe substrate, and is approximately flat; and a gas barrier layer thatis formed of an inorganic compound and covers the organic buffer layerin order to protect the plurality of light-emitting elements againstair. In the gas barrier layer, a portion that covers the region wherethe plurality of light-emitting elements are formed is thicker than aperipheral portion that covers end portions of the organic buffer layer.

In the light-emitting device, since the plurality of light-emittingelements are disposed on the substrate with gaps therebetween, the stepdifference occurs on a first surface of the organic buffer layer thatcovers the plurality of light-emitting elements. However, in the organicbuffer layer, the step difference on a second surface is smaller thanthat on the first surface. Accordingly, as compared with the case inwhich the organic buffer layer is not provided, the gas barrier layerbecomes further planarized on the plurality of light-emitting elements.As a result, the gas barrier layer is not easily cracked or peeled off.Further, in the region where the plurality of light-emitting elementsare formed, thick portions of the gas barrier layers overlap each other,the plurality of light-emitting elements can be reliably sealed. Inaddition, even if the gas barrier layers are not thin or flat, the gasbarrier layers are not easily cracked or peeled off. In addition, sincethe organic buffer layer is formed of an organic compound in which thestress can be easily dispersed, the gas barrier layers are not easilycracked or peeled off even if the gas barrier layers are thick. Asdescribed above, according to the light-emitting device, it is possibleto reliably seal the light-emitting elements with gas barrier layersthat are not easily cracked or peeled off.

Further, in the light-emitting device, preferably, in the end portionsof the organic buffer layer, an angle between an upper surface of theorganic buffer layer and the upper surface of the substrate is 20° orless.

According to the light-emitting device, in a portion where the totalthickness of the gas barrier layers is small, it is possible to makesufficiently small an angle by which the gas barrier layers are bent. Asa result, the stress concentration in the gas barrier layers issuppressed, which makes it difficult that the gas barrier layers crackor are peeled off.

Furthermore, according to still another aspect of the invention, anelectronic apparatus includes the above-described light-emitting device.In the light-emitting device, since it is possible to reliably seal thelight-emitting elements with the gas barrier layers that are not easilycracked or peeled off, it is possible to suppress the light-emittingelements from deteriorating. Therefore, according to the electronicapparatus, it is easy to keep the display quality for a long time.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a cross-sectional view illustrating an organic EL panelaccording to a first embodiment of the invention;

FIG. 2 is an enlarged cross-sectional view illustrating a part A shownin FIG. 1;

FIG. 3 is a cross-sectional view illustrating an organic EL panelaccording to a second embodiment of the invention;

FIG. 4 is an enlarged cross-sectional view illustrating a part B shownin FIG. 3;

FIG. 5 is a view illustrating a personal computer using the organic ELpanel according to the embodiment of the invention;

FIG. 6 is a view illustrating a mobile phone using the organic EL panelaccording to the embodiment of the invention;

FIG. 7 is a longitudinal sectional view illustrating an example of animage printing apparatus using the organic EL panel according to theembodiment of the invention; and

FIG. 8 is a longitudinal sectional view illustrating another example ofthe image printing apparatus using the organic EL panel according to theembodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of the invention will be describedwith reference to the accompanying drawings. Further, in order to makeeach layer and each member recognizable in the drawings, each layer andeach member have been reduced using different scales. Furthermore, sinceFIGS. 1 to 4 illustrate cross-sectional views, hatching is omittedexcept for some parts. That is, only some parts shown in FIGS. 1 to 4are hatched. In addition, in the following description, ‘on’ and ‘below’are used with the plane of the drawings as a reference, and a‘thickness’ of a layer refers to the length of the layer in the up/downdirection of the plane of the drawings.

A: First embodiment

An organic EL panel (light-emitting device) according to a firstembodiment of the invention is a full-color panel that uses apolymer-based organic EL material to be described later. In the organicEL panel, an organic EL element that emits red-colored light, an organicEL element that emits green-colored light, and an organic EL elementthat emits blue-colored light are disposed parallel to one another, suchthat full-color display can be performed. In addition, the organic ELpanel is a top-emission-type panel in which light from an organic ELelement is emitted from a side opposite to a main substrate.

A1: Configuration

FIG. 1 is a cross-sectional view illustrating the organic EL panel, andFIG. 2 is an enlarged cross-sectional view illustrating a part A of theorganic EL panel. The organic EL panel includes a plate-shaped mainsubstrate 10. The main substrate 10 is formed of glass or plastic, and aplurality of organic EL elements P1 are formed on the main substrate 10.The organic EL element P1 has an organic light-emitting layer 16 formedof a polymer-based organic EL material, which will be described later,and is supplied with electrical energy so that light can be emittedtherefrom (specifically, a light-emitting layer within the organiclight-emitting layer 16). The organic EL elements P1 are classified intothree kinds of organic EL element on the basis of the color of emittedlight. The three kinds of organic EL element P1 are regularly arrangedon the main substrate 10.

Further, a plurality of TFTs (thin film transistors) 11, whichcorrespond to the plurality of organic EL elements P1 in one-to-onemanner, and various wiring lines (only a part is shown) are formed onthe main substrate 10. Each of the TFTs 11 is supplied with electricalenergy and a control signal and drives the corresponding organic ELelement P1. Specifically, the TFTs 11 supply a current to the organic ELelements P1 at timings at which the organic EL elements P1 sequentiallyemit light. In addition, the inorganic insulating layer 12 that coversthe plurality of TFTs 11 is formed on the main substrate 10. Theinorganic insulating layer 12 is provided to insulate the plurality ofTFTs 11 and various wiring lines from one another and is formed of, forexample, silicon compound.

On the inorganic insulating layer 12, a lyophilic bank layer (inorganicpixel partition wall insulation layer) 13 is formed of, for example,silicon dioxide in a layer thickness of 50 to 200 nm. On the lyophilicbank layer 13, a lyophobic bank layer (organic pixel partition wallinsulation layer) 14 is formed of, for example, polyimide or acrylicresin in a layer thickness of 1 to 3 μm. The inorganic insulating layer12, the lyophilic bank layer 13, and the lyophobic bank layer 14 definerecessed portions, and the organic EL element P1 occupies a lowerportion of each of the recessed portions. In the case of alight-emitting device and an electronic apparatus in which a singlecolor is used, coating separation is not required, and accordingly, theorganic light-emitting layer 16 may be formed over anodes 15 and thelyophilic bank layer 13 by means of a spin coating method or a slitcoating method, as a structure in which the lyophobic bank layer 14 isnot formed.

The organic EL element P1 has the anode 15 and a common cathode layer 17with the organic light-emitting layer 16 interposed therebetween. Theanode 15 and the common cathode layer 17 serve as electrodes throughwhich holes and electrons are injected into the organic light-emittinglayer 16, and an electric field is generated between the anode 15 andthe common cathode layer 17 by means of electric energy supplied. Theanode 15 is an electrode that has work function of 5 eV or more and isformed of, for example, ITO into which holes can be easily injected, andthe anode 15 is connected to the corresponding TFT 11 by the wiringlines. The common cathode layer 17 is formed on the organiclight-emitting layer 16 and the lyophobic bank layer 14 and serves as acommon electrode with respect to the plurality of organic EL elementsP1. For example, the common cathode layer 17 has an electron injectionbuffer layer, which is provided to make electrons easy to inject intothe organic light-emitting layer 16, and a low-resistance layer that isformed on the electron injection buffer layer and is formed of a metalsuch as ITO or aluminum. The electron injection buffer layer is formedof, for example, lithium fluoride, calcium metal, or magnesium-silveralloy.

The organic light-emitting layer 16 includes a light-emitting layer thatemits light by excitation due to recombination of holes and electronsinjected by the electric field. Further, the organic light-emittinglayer 16 may have a multi-layered structure including layers other thanthe light-emitting layer, and in this case, it is preferable that alllayers be thin layers having a thickness of 300 nm or less in order toreduce an electrical resistance. The layers other than thelight-emitting layer include a hole injection layer that is provided foreasy injection of holes, a hole transport layer that is provided foreasy transport of the injected holes to the light-emitting layer, anelectron injection layer that is provided for easy injection ofelectrons, and an electron transport layer that is provided for easytransport of the injected electrons to the light-emitting layer, whichcontribute to the recombination of holes and electrons.

The light-emitting layer is formed of a polymer-based organic ELmaterial. The polymer-based organic EL material is an organic compoundhaving a relatively high molecular weight, among organic compounds thatemit light by excitation due to recombination of holes and electrons.The polymer-based organic EL material forming the organic EL element P1is formed of a material corresponding to the kind (color of emittedlight) of the organic EL element P1. A material of a layer contributingto the recombination in the light-emitting layer is chosen according toa material of a layer adjacent to the layer contributing to therecombination in the light-emitting layer. When these materials arediluted with solvent and are then pattern-coated in an inkjet printingmethod or other printing methods, a surface of the lyophobic bank layer14 repels a material of the organic light-emitting layer 16, and thusseparate coating of colors is performed for each pixel. In the case of asingle color in which the separate coating is not required, pixels canbe separated from one another by forming the organic light-emittinglayer 16 over the lyophilic bank layer 13 and the anodes 15 by means ofa spin coating method or a slit coating method, without forming thelyophobic bank layer 14. The lyophilic bank layer 13 is formed up toends of the anode 15, which is located at the lower portion of therecessed portion, and serves to stabilize the layer thickness of theorganic light-emitting layer 16, and the organic light-emitting layer 16is formed on the lyophilic bank layer 13. The lyophilic bank layer 13 isformed of, for example, silicon dioxide in a layer thickness of 50 to200 nm.

Furthermore, a cathode protection layer 18 that covers the commoncathode layer 17 is formed on the inorganic insulating layer 12 and thecommon cathode layer 17. In addition, in order to planarize unevennessdue to pixels, an organic buffer layer 19 is formed on the cathodeprotection layer 18 so as to completely cover the plurality of organicEL elements P1. In addition, a first gas barrier layer 20, whichcompletely covers the organic buffer layer 19 up to end portions of theorganic buffer layer 19, is formed on the cathode protection layer 18and the organic buffer layer 19 over an area larger than that of theorganic buffer layer 19. On the first gas barrier layer 20, a second gasbarrier layer 21 is formed over an area that is larger than that of theplurality of organic EL elements P1 and is smaller than that of theorganic buffer layer 19.

The first gas barrier layer 20 and the second gas barrier layer 21 areformed of a material having excellent light transmittance, gas barrierproperty, and water resistance. As an example of such a material, asilicon compound containing nitrogen, such as silicon oxynitride,silicon nitride, or SiNH, may be preferably used. A high-density plasmafilm deposition method, such as sputtering, ion plating, or CVD(chemical vapor deposition), using ICP or ECR (electron cyclotronresonance) plasma or high-density plasma generated by a plasma gin maybe used as a method of forming the gas barrier layer, and thus ahigh-density and high-quality thin film made of an inorganic compoundcan be formed at a low temperature. The first gas barrier layer 20 helpsthe organic buffer layer 19 and the plurality of organic EL elements P1to be reliably sealed. The thickness of the first gas barrier layer 20is within a range of 200 to 400 mm. The lower limit of the range isdetermined such that side surfaces of the organic buffer layer 19 or theneighborhood thereof are not insufficiently sealed. The second gasbarrier layer 21 helps the plurality of organic EL elements P1 to bereliably sealed. The thickness of the second gas barrier layer 21 iswithin a range of 200 to 800 nm. Further, in the present embodiment, thethickness of the first gas barrier layer 20 and the thickness of thesecond gas barrier layer 21 are limited such that the sum of thethickness of the first gas barrier layer 20 and the thickness of thesecond gas barrier layer 21 is less than 1000 nm. The limitation isdetermined in consideration of the sealing reliability with respect tothe plurality of organic EL elements P1, a possibility, that the gasbarrier layer will crack or be peeled off, and a manufacturing cost.

The organic buffer layer 19 is provided to improve planarization andadhesion of the first gas barrier layer 20 and to relieve stressoccurring in the first gas barrier layer 20, and the organic bufferlayer 19 is formed by curing a material for an organic buffer layer(hereinafter, simply referred to as ‘organic buffer layer material’)which has viscosity and composition to be described later, in alow-pressure atmosphere. An upper surface of the organic buffer layer 19that covers the plurality of organic EL elements P1 is flat. In each ofthe end portions of the organic buffer layer 19, an angle θ1 between theupper surface of the organic buffer layer 19 and an upper surface of themain substrate 10 is 20° or less. The thickness of the organic bufferlayer 19, which covers the plurality of organic EL elements P1,excluding the vicinities of the end portions is within a range of 3 to10 μm. The organic buffer layer 19 is formed by using a screen printingmethod. In the screen printing method, a mesh and a squeegee are usedsuch that unevenness due to pixel partition walls can be solved bycontrolling the layer thickness. As a result, it is possible toplanarize the upper surface of the organic buffer layer 19. The lowerlimit of the thickness of the organic buffer layer 19 is determined inconsideration of the height of the pixel partition walls and the sealingreliability with respect to fine contamination that has adhered onto thesubstrate in previous processes. The upper limit of the thickness of theorganic buffer layer 19 is determined such that the angle at each of theend portions of the organic buffer layer 19 is 20° or less and an amountof light, which leaks from a side surface of a surface protectionsubstrate 23 or a side surface of an adhesion layer 22, which will bedescribed later, without reaching an upper surface of the surfaceprotection substrate 23, is not excessively high.

The cathode protection layer 18 is provided to protect the commoncathode layer 17 and to improve the wettability and adhesion of theorganic buffer layer 19 before the organic buffer layer 19 is cured, andthe cathode protection layer 18 is formed of silicon compound, such assilicon oxynitride, having excellent light transmittance, adhesion, andwater resistance. In particular, in the case where the common cathodelayer 17 has a top emission structure, the layer thickness of the commoncathode layer 17 is made small in consideration of transparency, whichincreases frequency of generation of pin holes, for example. For thisreason, since a small amount of moisture, which is adhered while amaterial of the organic buffer layer 19 is being deposited until theorganic buffer layer 19 is completely formed, and the material of theorganic buffer layer 19 permeated into the organic light-emitting layer16 causes the organic light-emitting layer 16 to be damaged and thedamaged portion of the organic light-emitting layer 16 becomes a darkspot, the cathode protection layer 18 serves to prevent the damage. Inaddition, on the upper surface of the common cathode layer 17,unevenness exists due to the step difference between the lyophobic banklayer 14 and the organic EL element P1, which causes stress to beconcentrated in the cathode protection layer 18. In order to preventdamage due to the stress concentration, the thickness of the cathodeprotection layer 18 is set to 200 mm or less.

Furthermore, on the main substrate 10, the adhesion layer 22 is formedto cover the inorganic insulating layer 12, the cathode protection layer18, the first gas barrier layer 20, and the second gas barrier layer 21.The surface protection substrate 23 is provided on the adhesion layer 22so as to completely cover the adhesion layer 22. The entire lowersurface of the surface protection substrate 23 is adjacent to theadhesion layer 22. The adhesion layer 22 is provided for adhesionbetween the surface protection substrate 23 and the main substrate 10and is formed of resin adhesive having excellent light transmittance.Examples of the resin adhesive include epoxy resin, acrylic resin,urethane resin, silicon resin, or the like. The surface protectionsubstrate 23 is provided to improve optical characteristics and toprotect the gas barrier layer and is formed of glass or plastic havingexcellent light transmittance. Examples of the plastic includepolyethyleneterephthalate, acrylic resin, polycarbonate, polyolefin, orthe like. In addition, the surface protection substrate 23 may have afunction of a color filter, a function of blocking/absorbing ultravioletrays, a function of preventing reflection of external light, or afunction of heat dissipation using a fin.

A2: Manufacturing Process

In order to manufacture an organic EL panel according to the presentembodiment, first, the TFTs 11, various wiring lines, and the inorganicinsulating layer 12 are formed on the main substrate 10. Then, areflective layer, which has a light-reflective property and is formedof, for example, an aluminum-copper alloy material, and transparent ITOare deposited on or below the inorganic insulating layer 12 by using asputtering method, thereby forming the anodes 15 serving as a pluralityof pixels. An upper surface of the anode 15 adjacent to the organiclight-emitting layer 16 is preferably formed of ITO having a high workfunction in consideration of injection of holes. Accordingly, the TFTs11 and the anodes 15 are connected to each other in one-to-one manner.Then, the lyophilic bank layer 13 is formed on the inorganic insulatinglayer 12 so as to surround the anodes 15. Then, the lyophobic bank layer14, which is formed of an organic compound, such as polyimide or acrylicresin, is formed on the lyophilic bank layer 13. Then, a washingprocess, such as plasma washing, is performed to remove organiccontamination from the main substrate and to improve the wettability ofthe ITO surface.

Thereafter, the organic light-emitting layer 16 is formed on the anodes15. In this process, when a material of the organic light-emitting layer16 is coated, the material spreads out to be flat adjacent to thelyophilic bank layer 13. Thus, the organic light-emitting layer 16 thatis flat and has a uniform thickness is formed. In a process of formingthe light-emitting layer included in the organic light-emitting layer16, a polymer-based organic EL material used to form the organiclight-emitting layer 16 that generates red-colored light is coated onthe anode 15 which is to form the organic EL element P1 that generatesthe red-colored light. The same process as above is performed for theorganic EL element P1 that generates green-colored light and the organicEL element P1 that generates blue-colored light. Furthermore, in thecase of a single color, it takes a short time to perform a coatingprocess if a spin coating method or a slit coating method is used. Onthe other hand, in the case of coating and separating three kinds ofcolored materials, it is preferable to perform pattern coating for eachpixel by using an inkjet printing method or a screen printing method interms of efficiency of use of materials. When the organic light-emittinglayer 16 has a plurality of layers, the plurality of layers aresequentially formed.

Then, an electrode common to the plurality of organic EL elements P1,that is, the common cathode layer 17 is formed. For example, a metal oralloy into which electrons can be easily injected, such as lithiumfluoride, calcium, or magnesium, is deposited by means of a vacuumdeposition method using a heating boat (crucible). Then, in order toreduce the resistance of the common electrode, aluminum is deposited soas to avoid pixel units by means of the vacuum deposition method ortransparent ITO is deposited at low-pressure atmosphere by means of ahigh-density plasma deposition method, such as an ECR plasma sputteringmethod, an ion plating method, or an opposite target sputtering method.Then, an oxygen plasma process is performed, and then the cathodeprotection layer 18, which is formed of silicon oxynitride, is formed soas to cover the common cathode layer 17 by means of the high-densityplasma deposition method, such as the ECR plasma sputtering method orthe ion plating method, in the same manner as for the ITO. Here, theoxygen plasma process is performed to improve the adhesion between thecommon cathode layer 17 and the cathode protection layer 18.

Subsequently, an organic buffer layer material having liquid form, whichhas viscosity of 2000 to 10000 mPa·s at room temperature (25° C.), isprinted on the cathode protection layer 18 by using a screen printingmethod in a low-pressure atmosphere, nitrogen gas is introduced for thechange to atmospheric pressure, and then the organic buffer layermaterial is carried to a curing chamber in which the organic bufferlayer material corresponding to each substrate is heated at thetemperature of 60 to 100° C. such that the organic buffer layer materialis completely cured, thereby forming the organic buffer layer 19. Thereason why the process of forming the organic buffer layer 19 isperformed in the low-pressure atmosphere is to remove moisture andbubbles generated at the time of a coating process. That is, unlike inthe process of forming the common cathode layer 17 or the cathodeprotection layer 18, while the organic buffer layer material is coatedin a relatively low vacuum condition of 100 to 5000 Pa, the moisture isremoved until a dew point reaches 60° C. or less by introducingnitrogen. In addition, the reason why the organic buffer layer materialhaving a viscosity of 2000 mPa·s or more at room temperature is used isto avoid permeation of organic buffer layer material into the commoncathode layer 17 or the organic light-emitting layer 16 through thecathode protection layer 18.

As a main component (for example, 70% or more by weight) of the organicbuffer layer material, it is possible to use an organic compound whichhas good fluidity before being cured and does not have a volatilecomponent such as solvent. In the present embodiment, an epoxy monomer(molecular weight of 3000 or less) that contains an epoxy group and hasa molecular weight of 3000 or less/oligomer (molecular weight of 1000 to3000) are used as the main component of the organic buffer layermaterial. Specifically, bisphenol A type epoxy oligomer or bisphenol Ftype epoxy oligomer, phenol novolac type epoxy oligomer,3,4-epoxycyclohexenylmethyl-3′,4′-epoxycyclohexenecarboxylate,caprolactone-modified3,4-epoxycyclohexenylmethyl-3′,4′-epoxycyclohexenecarboxylate or thelike can be used alone or in combination.

As a sub-component of the organic buffer layer material, a curing agentthat reacts with the epoxy monomer/oligomer may be used. In this case,it is preferable to use a curing agent capable of forming a cured layerthat has a good insulation property, high heat resistance, and highstrength. In addition, it is preferable to use anadditive-polymerization-type curing agent having good lighttransmittance and small deviation in the cured state. Specifically, itis preferable to use an acid anhydride based curing agent formed of, forexample, 3-methyl-1,2,3,6-tetrahydrophthalic anhydride,methyl-3,6-endomethylene-1,2,3,6-tetrahydrophthalic anhydride,1,2,4,5-benzenetetracarboxylic dianhydride,3,3′,4,4′-benzophenonetetracarboxylic dianhydride, or a polymerizedmaterial thereof. The first reason why the acid anhydride based curingagent is preferably used is that the acid anhydride based curing agentis cured by heat treatment within the temperature range of 60 to 100 Cand the cured layer becomes a polymer that has good adhesion withrespect to silicon oxynitride and has an ester bond. The second reasonis that the acid anhydride based curing agent can be cured at lowtemperature within a short period of time by adding a curing acceleratorfor accelerating the ring-opening of acid anhydride, such as aromaticamines, alcohols, and aminophenol, which have a relatively highmolecular weight. The third reason is that it is difficult to cause theacid anhydride based curing agent to be easily damaged due tocontraction when performing a rapid curing process, as compared withcation-emission-type photopolymerization initiator.

As other sub-components of the organic buffer layer material, additives,such as a silane coupling agent for improving the adhesion between theorganic buffer layer 19 and the common cathode layer 17 or the first gasbarrier layer 20, a water supplementing agent such as an isocyanatecompound, and particles for preventing contraction when curing theorganic buffer layer 19, are mixed in the organic buffer layer material.

The viscosity of each of the main component materials and thesub-component materials used in the present embodiment, before beingcured, is preferably 1000 mPa·s or more at room temperature. This is toreduce a possibility that the materials will permeate into the organiclight-emitting layer 16 before being cured. The viscosity of thesematerials should be determined in consideration of the reduction of theabove possibility, whether the organic buffer layer 19 can be formed atthe required pattern precision, whether the organic buffer layer 19 canbe formed with a desired thickness, whether bubbles are not generated inthe formed organic buffer layer 19, or the like.

Then, an oxygen plasma process is performed in the low-pressureatmosphere and a high-density plasma deposition method, such as the ECRsputtering method or the ion plating method, is performed such that theorganic buffer layer 19 is completely covered up to end portions of theorganic buffer layer 19 over an area larger than that of the organicbuffer layer 19, thereby forming the first gas barrier layer 20. Thereason why the oxygen plasma process is performed is to improve theadhesion between the organic buffer layer 19 and the first gas barrierlayer 20. Then, by using a high-density plasma deposition method, suchas the ECR sputtering method or the ion plating method, the second gasbarrier layer 21 is formed on the first gas barrier layer 20 such thatthe plurality of organic EL elements P1 are covered and the end portionsof the organic buffer layer 19 are not covered.

Thereafter, under atmospheric pressure, a resin adhesive havingexcellent light transmittance is coated to cover the inorganicinsulating layer 12, the cathode protection layer 18, the first gasbarrier layer 20, and the second gas barrier layer 21, the entire lowersurface of the surface protection substrate 23 comes in contact with theresin adhesive, and the resin adhesive is cured, thereby forming theadhesion layer 22. Alternatively, an adhesive having liquid form may beused instead of the resin adhesive or a sheet-shaped adhesive may beinterposed between the second gas barrier layer 21 and the surfaceprotection substrate 23 and be then pressed therebetween.

A3: Effects

In the organic EL panel according to the present embodiment, on theplurality of organic EL elements P1, the uneven level of the uppersurface of the organic buffer layer 19 is smaller than that of the uppersurface of the cathode, that is, the upper surface of the organic bufferlayer 19 is approximately flat. Therefore, as compared with a structurein which the organic buffer layer 19 is not provided, on the pluralityof organic EL elements P1, the first gas barrier layer is furtherplanarized and the stress concentration is suppressed, and accordingly,the gas barrier layer is not easily cracked or peeled off. Further, overthe entire plurality of organic EL elements P1, since the first gasbarrier layer 20 and the second gas barrier layer 21 overlap each other,the total thickness of the gas barrier layers is sufficiently large. Asa result, the plurality of organic EL elements P1 can be reliablysealed. On the other hand, in portions of the first gas barrier layer 20not overlapping the second gas barrier layer 21, the thickness of thegas barrier layer is small. However, since the end portions of theorganic buffer layer 19 exist in the portions of the first gas barrierlayer 90 not overlapping the second gas barrier layer 21, the gasbarrier layer 20 is not easily cracked or peeled off even if unevennessis generated on a surface of the gas barrier layer. In addition, sincethe main component of the material for the organic buffer layer 19 is anorganic compound, the stress can be easily buffered. Accordingly, itbecomes more difficult for the gas barrier layer 20 to be easily crackedor peeled off. As such, according to the organic EL panel, the pluralityof organic EL elements P1 can be sufficiently sealed by means of the gasbarrier layers that are not easily cracked or peeled off. The stressthat is buffered by the organic buffer layer 19 includes stress due to aforce applied from the outside of the organic EL panel, stress due toexpansion and contraction, which occur due to temperature variation, ofthe lyophobic bank layer 14 formed of an organic compound, or the like.

In the organic EL panel, the plurality of organic EL elements arerequired to be reliably sealed. For example, in the case when an organiclight-emitting layer includes an electron injection layer, if moisturepermeates into the electron injection layer of one of the organic ELelements, the moisture prohibits the organic EL element from emittinglight, which may cause a so-called dark spot. Accordingly, in theorganic EL panel according to the present embodiment, the totalthickness of the gas barrier layers on the plurality of organic ELelements P1 is set to be large. Here, both the first gas barrier layer20 and the second gas barrier layer 21 are not made thick, but only thesecond gas barrier layer 21 is made thick. As a result, according to theorganic EL panel, it is possible to make the first gas barrier layer 20so as to be not easily cracked or peeled off and to make the pluralityof organic EL elements P1 reliably sealed, without making the first gasbarrier layer 20 thick.

If the portions of the first gas barrier layer 20 not overlapping thesecond gas barrier layer 21 crack or are peeled off, the sealingreliability with respect to the plurality of organic EL elements P1 isnoticeably reduced. Among the portions of the first gas barrier layer 20not overlapping the second gas barrier layer 21, a portion, in which thefirst gas barrier layer 20 extends with the cathode protection layer 18while being separated from the cathode protection layer 18, that is, theneighborhood of the end portions of the organic buffer layer 19 has alarge bent angle. In the organic EL panel according to the presentembodiment, the angle θ1 between the lower surface of the first gasbarrier layer 20 and the upper surface of the main substrate 10 is 20°or less in the end portions of the organic buffer layer 19. Accordingly,it is possible to suppress the stress concentration in the gas barrierlayer and to make the gas barrier layer so that it is not easily crackedor peeled off.

As described above, the gas barrier layer in the organic EL panelaccording to the present embodiment is not easily cracked or peeled off.As a result, since the sealing reliability with respect to the pluralityof organic EL elements P1 can be kept high, the period of time for whichthe organic EL panel can reliably emit light becomes long. In order tosupport this, an experiment was performed in which various organic ELpanels according to the present embodiment and other organic EL panelswere exposed for 600 consecutive hours at the temperature of 60° C. andin an atmosphere with RH (relative humidity) of 90% and then theemission states of those organic EL panels were examined. Each of theorganic EL panels used in this experiment has an organic buffer layer,which is formed of epoxy resin and has a thickness of 5 μm, and a gasbarrier layer that is formed of silicon oxynitride and is formed over alarge region so that end portions of the organic buffer layer arecompletely covered.

The result of the experiment is as follows. In the case of an organic ELpanel having only one gas barrier layer having a thickness of 800 m,some of the plurality of organic EL elements close to a peripheralportion (end portions of the organic buffer layer) showed emissionfailure. Furthermore, in the case of an organic EL panel which has twogas barrier layers each having a thickness of 400 nm and in which aregion on the main substrate overlapping a lower one of the gas barrierlayers is the same as a region on the main substrate overlapping anupper one of the gas barrier layers, some of the plurality of organic ELelements located in the peripheral portion showed emission failure. Inboth the organic EL panels, the reason why the organic EL elementslocated in the peripheral portion showed the emission failure is that agas barrier layer near a tapered portion of the organic buffer layercracked or was peeled off so that moisture permeated into the organic ELelements.

On the other hand, like the organic EL panel according to the presentembodiment, in the case of an organic EL, panel which has two gasbarrier layers each having a thickness of 400 nm and in which a lowerone of the gas barrier layers having the thickness of 400 nm is formedto completely cover the organic buffer layer up to end portions of theorganic buffer layer and an upper one of the gas barrier layers havingthe thickness of 400 nm is formed over an area smaller than that of theorganic buffer layer so that the end portions of the organic bufferlayer can be exposed, all of the plurality of organic EL elements showedgood emission states. Further, like the organic EL panel according tothe present embodiment, in the case of an organic EL panel which has agas barrier layer having a thickness of 200 nm and another gas barrierlayer formed on the gas barrier layer with a thickness of 700 nm and inwhich a lower one of the gas barrier layers is formed to completelycover the organic buffer layer up to end portions of the organic bufferlayer and an upper one of the gas barrier layers is formed over an areasmaller than that of the organic buffer layer so that the end portionsof the organic buffer layer can be exposed, all of the plurality oforganic EL elements showed good emission states.

As a method of sealing the organic EL elements, a method of using acap-shaped sealing substrate is known. On the other hand, the organic ELpanel is demanded to be large, thin, and light. In order to meet thesedemands, it is difficult to realize an organic EL panel havingsufficient strength against external stress because the peripheralportion and the main substrate are held by adhesive in the method ofusing the cap-shaped sealing substrate. In contrast, in the organic ELpanel according to the present embodiment, the plurality of organic ELelements P1 are sealed over a large area by means of the so-called thinfilm sealing method. Accordingly, the strength of the panel is veryhigh, it is difficult for the gas barrier layer to crack or be peeledoff; and the sealing reliability with respect to the plurality oforganic EL elements P1 is sufficiently high. As a result, according tothe organic EL panel, it is possible to meet the above demands for thelarge, thin, and light organic EL panel. Further, as the organic ELpanel becomes large, numbers of TFTs and wiring lines between theorganic EL elements and the main substrate increase. As a result, in thecase of a bottom-emission-type organic EL panel in which light from anorganic light-emitting layer is emitted from the main substrate side,the aperture ratio of a pixel is reduced, which may cause the emissionefficiency to be lowered. However, since the organic EL panel accordingto the present embodiment is of a top emission type, there is nopossibility that the emission efficiency will be lowered.

When manufacturing the organic EL panel, it is preferable to perform aprocess under a high vacuum condition of 1 Pa or less in order toprevent adhesion of contamination, such as dust, or moisture. However,since the organic buffer layer material is of a liquid type, it isdifficult to form the organic buffer layer 19 under the high vacuumcondition. Therefore, in the present embodiment, the organic bufferlayer 19 is formed using a screen printing method in a low-pressureatmosphere of 100 to 5000 Pa. This removes contamination and bubblesgenerated at the time of a coating process, contributing to removing pinholes in the gas barrier layer. In addition, the gas barrier layer isformed under a high vacuum condition of 0.1 to 10 Pa and at lowtemperature by means of a high-density plasma deposition method.Accordingly, the formation of the gas barrier layer is completed withoutdamaging the plurality of organic EL elements P1. In addition, as isapparent from the above-described manufacturing process, the sealingprocess of the organic EL panel is not affected by the contaminationthat cannot be blocked even in a clean room. This is a ver, advantageousfeature of the invention, as compared with actual circumstances in whichit is difficult to perform a washing process until the sealing processis completed once a process of forming the organic buffer layer starts.

B: Second Embodiment

An organic EL panel according to a second embodiment of the invention isa full-color panel that uses a low-molecular-weight-based organic ELmaterial to be described later. In the organic EL panel, full-colordisplay is performed by using a color filter and an organic EL elementthat emits white light. In addition, the organic EL panel is atop-emission-type panel in which light from an organic EL element isemitted from a side opposite to a main substrate.

B1: Configuration

FIG. 3 is a cross-sectional view illustrating the organic EL panel, andFIG. 4 is an enlarged cross-sectional view illustrating a part B of theorganic EL panel. A main substrate 30 is formed of glass or plastic, anda plurality of organic EL elements P2 are formed on the main substrate30. The organic EL element P2 is an element that emits white light, hasan organic light-emitting layer 37 formed of alow-molecular-weight-based organic EL material, which will be describedlater, and is supplied with electrical energy so that light can beemitted from the organic light-emitting layer 37 (specifically, alight-emitting layer within the organic light-emitting layer 37).

Further, a plurality of TFTs 31, which correspond to the plurality oforganic EL elements P2 in one-to-one manner, and various wiring lines(not shown) are formed on the main substrate 30. In the same manner asthe TFTs 11 in the first embodiment, the TFTs 31 drive the correspondingorganic EL elements P2. In addition, the inorganic insulating layer 32that covers the plurality of TFTs 31 is formed on the main substrate 30.The inorganic insulating layer 32 is provided to insulate the pluralityof TFTs 31 and various wiring lines from one another and is formed of,for example, silicon nitride.

Furthermore, a planarizing layer 33 is formed on the inorganicinsulating layer 32. The planarizing layer 33 is provided to makeoptical paths from light-emitting layers equal to one another byremoving the step difference due to wiring lines or TFTs and is formedof an organic compound, such as polyimide or acrylic resin. An uppersurface of the planarizing layer 33 has unevenness. Protruding portionshave flat upper surfaces and overlap the plurality of organic ELelements P2. Recessed portions overlap the plurality of TFTs 31. Withinthe planarizing layer 33, a metal reflection layer 34 that reflectslight incident from the organic EL elements P2 through anodes 35 isformed of a light-reflective metal.

On the planarizing layer 33, a pixel partition wall insulation layer 36that goes up from the recessed portions of the planarizing layer 33 isformed of an organic compound, such as polyimide or acryl. An upper endof the pixel partition wall insulation layer 36 is positioned to behigher than the protruding portions of the planarizing layer 33, and theplanarizing layer 33 and the pixel partition wall insulation layer 36define the recessed portions. Portions, in which the pixel partitionwall insulation layer 36 does not exist and the anodes 35 are in contactwith the organic light-emitting layer 37, become the organic EL elementsP2.

The organic EL elements P2 have the plurality of anodes 35 and a commoncathode layer 38 with the organic light-emitting layer 37 interposedtherebetween. The anodes 35 and the common cathode layer 38 serve aselectrodes through which holes and electrons are injected into theorganic light-emitting layer 37. The anode 35 is a transparent electrodethat is formed on the planarizing layer 33 and is formed of, forexample, ITO which has high work function and into which holes can beeasily injected, and the anode 35 is connected to the corresponding TFT31 through a gap between the planarizing layer 33 and the pixelpartition wall insulation layer 36. The common cathode layer 38 isformed on the organic light-emitting layer 37 and the pixel partitionwall insulation layer 36 and serves as a common electrode with respectto the plurality of organic EL elements P2. For example, the commoncathode layer 38 has an electron injection buffer layer, which isprovided to make electrons easily injected into the organiclight-emitting layer 37, and a low-resistance layer, such as atransparent ITO layer formed on the electron injection layer or analuminum layer that is formed on a non-pixel region. The electroninjection buffer layer is formed of, for example, lithium fluoride ormagnesium-silver alloy.

The organic light-emitting layer 37 corresponds to the organiclight-emitting layer 16 in the first embodiment. The difference betweenthe organic light-emitting layer 37 and the organic light-emitting layer16 is that the organic light-emitting layer 37 is common to theplurality of organic light-emitting layers 37 and is formed of alow-molecular-weight-based organic EL material. Thelow-molecular-weight-based organic EL material is an organic compoundhaving a relatively low molecular weight, among organic compounds thatemit light by excitation due to recombination of holes and electrons.For example, the low-molecular-weight-based organic EL material includesa material obtained by doping anthracene-based impurities intostyrylamine-base host or a material obtained by doping rubrene-basedimpurities into styrylamine-base host. When the organic light-emittinglayer 37 includes an additional layer contributing to the recombinationin the light-emitting layer, a material of the additional layer isdetermined according to a material of a layer adjacent to the additionallayer. For example, a material of the hole injection layer includestriallylamine (ATP) polymer, a material of the hole transport layerincludes triphenyl diamine (TPD) based compound, and a material of theelectron injection layer includes aluminum quinolinol complex.

Furthermore, a cathode protection layer 39 that covers the commoncathode layer 38 and the planarizing layer 33 is formed on the inorganicinsulating layer 32 and the common cathode layer 38. In addition, anorganic buffer layer 40 is formed on the cathode protection layer 39 soas to completely cover the plurality of organic EL elements P2, thepixel partition wall insulation layer 36, the planarizing layer 33. Inaddition, a first gas barrier layer 41, which completely covers theorganic buffer layer 40 up to end portions of the organic buffer layer40, is formed on the cathode protection layer 39 and the organic bufferlayer 40. On the first gas barrier layer 41, a second gas barrier layer42 is formed so as to cover the entire plurality of organic EL elementsP2 and to cover a region smaller than the organic buffer layer 40 sothat the end portions of the organic buffer layer 40 can be exposed.

The cathode protection layer 39, the organic buffer layer 40, the firstgas barrier layer 41, and the second gas barrier layer 42 correspond tothe cathode protection layer 18, the organic buffer layer 19, the firstgas barrier layer 20, and the second gas barrier layer 21, respectively.Even though parts of the organic buffer layer 40, the first gas barrierlayer 41, and the second gas barrier layer 42 overlapping the entireplurality of organic EL elements P2 are flat, the flatness is lower thanthat in the first embodiment. This is because the thickness of theorganic buffer layer 40 is 3 to 5 μm, the thickness is not sufficient torealize the same flatness as in the first embodiment. However,unevenness of the upper surface of the organic buffer layer 40 is 0.5 μmor less, and an uneven level of upper surface of the organic bufferlayer 40 is extremely smaller than that of the upper surface of thecommon cathode layer 38. Further, when a screen printing method used toform the organic buffer layer 40 is used, it is possible to make theuneven level of the upper surface of the organic buffer layer 40 smallerby making planarization control using a screen mesh and a squeegee.

Furthermore, on the main substrate 30, an adhesion layer 43 is formed tocover the inorganic insulating layer 32, the cathode protection layer39, the first gas barrier layer 41, and the second gas barrier layer 42.In addition, a color filter substrate 44 is provided on the adhesionlayer 43 so as to completely cover the adhesion layer 43. The entirelower surface of the color filter substrate 44 is adjacent to theadhesion layer 43. The adhesion layer 43 is provided for adhesionbetween the color filter substrate 44 and the main substrate 30 and isformed of resin adhesive having excellent light transmittance. The resinadhesive includes epoxy resin, acrylic resin, urethane resin, siliconresin, or the like. The adhesion layer 43 may be composed of two kindsof different adhesives. In this case, preferably, an ultraviolet-settingadhesive is used in a peripheral region, and a thermosetting adhesive isused in an emission surface located at a central portion. Further, it isessential to precisely control the position of the color filtersubstrate and the thickness of the adhesive. Since theultraviolet-setting adhesive can be cured for only a few seconds withoutposition deviation, the position control or the thickness control can beeasily made.

The color filter substrate 44 is provided to extract red-colored,green-colored, and blue-colored light components from light emitted fromthe organic EL elements P2 and includes a black matrix layer 45 havinglow light transmittance and filter layers 46 that cover openings formedin the black matrix layer 45. The black matrix layer 45 has a pluralityof openings. In addition, three kinds of filter layers 46, which includea filter layer through which only red-colored light is transmitted, afilter layer through which only green-colored light is transmitted, anda filter layer through which only blue-colored light is transmitted.Each of the filter layers 46 overlaps the organic EL elements P2. Thered-colored, green-colored, and blue-colored light components of thelight emitted from the organic EL elements P2 overlapping the filterlayers 46 are transmitted through the corresponding filter layers 46,respectively. Furthermore, since the color filter substrate 44 serves toprotect a gas barrier layer, a portion other than the black matrix layer45 and the filter layers 46 is formed of glass or plastic havingexcellent light transmittance. The plastic includespolyethyleneterephthalate, acrylic resin, polycarbonate, polyolefin, orthe like. In addition, the color filter substrate 44 may have a functionof blocking/absorbing ultraviolet rays, a function of preventingreflection of external light, or a function of heat dissipation.

B2: Manufacturing Process

In order to manufacture the organic EL panel according to the presentembodiment, first, the TFTs 31, various wiring lines, and the inorganicinsulating layer 32 are firmed on the main substrate 30. Then, theplanarizing layer 33 and the metal reflection layer 34 are formed on theinorganic insulating layer 32. Then, in order to prevent electricalcorrosion of the metal reflection layer 34, a surface and a peripheralportion of the metal reflection layer 34 are coated with an inorganicinsulating layer, and then the plurality of anodes 35 are formed. Thus,the TFTs 31 and the anodes 35 are connected to each other in one-to-onemanner. As a method of forming the anodes, it is possible to use one ofthe known methods suitable for a material of the anodes 35. Then, thepixel partition wall insulation layer 36 is formed on parts of theanodes 35 and the planarizing layer 33 by means of pattern formation ofpolyimide, for example. Then, a washing process, such as a plasmawashing, is performed to remove organic contamination from the mainsubstrate 30 or to increase the work function.

Thereafter, on the anodes 35 that are exposed, the organiclight-emitting layer 37 common to the plurality of organic EL elementsP2 is formed. In this process, a light-emitting layer is formed with alow-molecular-weight-based organic EL material. The process of formingthe organic light-emitting layer 37 is performed using a vacuumdeposition method using a heating boat. The vacuum deposition method canalso be applied to a case in which the organic light-emitting layer 37includes only a light-emitting layer or a case in which the organiclight-emitting layer 37 includes a plurality of layers. In the case whenthe organic light-emitting layer 37 includes the plurality of layers,the plurality of layers are sequentially formed.

Then, an electrode common to the plurality of organic EL elements P2,that is, the common cathode layer 38 is formed. Then, an oxygen plasmaprocess is performed, and then the cathode protection layer 39 is formedto cover the common cathode layer 38. Then, the organic buffer layer 40is formed on the cathode protection layer 39 by using a screen printingmethod in a low-pressure atmosphere. Then, an oxygen plasma process isperformed and then the first gas barrier layer 41 is formed over an arealarger than that of the organic buffer layer 40 so as to cover theentire organic buffer layer 40. Then, on the first gas barrier layer 41,a second gas barrier layer 42 is formed so as to overlap the entireplurality of organic EL elements P2 and to cover a region smaller thanthe organic buffer layer 40 so that the end portions of the organicbuffer layer 40 can be exposed. Materials or methods of forming theorganic buffer layer 40, the first gas barrier layer 41, and the secondgas barrier layer 42 are the same as described in the first embodiment.

Subsequently, a resin adhesive having excellent light transmittance iscoated to cover the inorganic insulating layer 32, the cathodeprotection layer 39, the first gas barrier layer 41, and the second gasbarrier layer 42, the entire lower surface of the color filter substrate44 comes in contact with the resin adhesive, and the resin adhesive iscured, thereby forming the adhesion layer 43. This curing is performedat the locations at which the plurality of filters 46 of the colorfilter substrate 44 overlap the plurality of organic EL elements P2 inone-to-one manner. In addition, the alternative of adhesion of thesurface protection substrate 23 in the first embodiment can also beapplied as alternative of adhesion of the color filter substrate 44.

B3: Effects

In the organic EL panel according to the present embodiment, it ispossible to obtain the same effects as obtained in the organic EL panelaccording to the first embodiment.

C: Modifications

In a modification of the above-described embodiment, it is possible touse a panel that emits single colored light or a full-color panel havinga color conversion layer. Alternatively, a bottom-emission-type panelmay be used. In this case, the requirement of high light transmittanceis limited to layers located below the light-emitting layer.Accordingly, when the common cathode layer is located above thelight-emitting layer, the common cathode layer may be formed thick overthe entire surface of a substrate by using a metal material, such aslow-resistance aluminum.

In another modification of the above-described embodiment, the secondgas barrier layer may be located below the first gas barrier layer, orthe second gas barrier layer may be located within the organic bufferlayer. Further, the number of gas barrier layers may be 3 or more. Atthis time, these gas barrier layers should include at least one gasbarrier layer that is formed over an area smaller than that of theorganic buffer layer so that end portions of the organic buffer layercan be exposed.

In still another modification of the above-described embodiment, onlyone gas barrier layer may be provided. At this time, the gas barrierlayer should be formed such that the organic buffer layer is covered anda portion completely overlapping the plurality of organic EL elements isthicker than other portions that cover the end portions of the organicbuffer layer. A method of forming the gas barrier layer can bearbitrarily selected. For example, the gas barrier layer may be formedby using a deposition source disposed to be close to the center of theplurality of organic EL elements, or the gas barrier layer may be formedby forming a gas barrier layer having uniform thickness and then etchingportions not overlapping the organic EL elements such that the portionsnot overlapping the organic EL elements become thin.

D: Electronic Apparatus

The above-mentioned organic EL panel can be applied to variouselectronic apparatuses. In the invention, the organic EL panel isapplied to an image display apparatus and an image printing apparatus.

D1: Image Display Apparatus

An image display apparatus having the organic EL panel includes wiringlines for supplying electric energy and control signals to the organicEL panel and a circuit for generating control signals allowing anoptical image to be formed on the organic EL panel on the basis of imagedata supplied from an external device. Various types of image displayapparatuses can be used, but in the invention, two types of imagedisplay apparatuses are exemplified.

FIG. 5 shows the structure of a personal computer using theabove-mentioned organic EL panel as a display unit 31. A personalcomputer 30 includes a display unit 31, serving as a display device, anda main body 32. The main body 32 is provided with a power switch 33 anda keyboard 34. Since the personal computer 30 uses the above-mentionedorganic EL panel as the display unit 31, it is possible to meet demandsfor an increase in the size of the display unit 31 and a reduction inthe thickness and weight of the display device 31. In addition, sincethe quality of light emitted from the organic EL panel is hardlydeteriorated, it is easy to keep display quality for a long time.

FIG. 6 shows the structure of a mobile phone using the above-mentionedorganic EL panel as a display unit 41. A mobile phone 40 includes aplurality of operating buttons 42, a plurality of scroll buttons 43, andthe display unit 41 serving as a display device. The scroll button 43 isoperated to scroll a screen displayed on the display unit 41. Since themobile phone 40 uses the above-mentioned organic EL panel as the displayunit 41, it is possible to meet demands for a reduction in the thicknessand weight of the display device 41. In addition, since the quality oflight emitted from the organic EL panel is hardly deteriorated, it iseasy to keep display quality for a long time.

D2: Image Printing Apparatus

Next, an image printing apparatus using the above-mentioned organic ELpanel will be described. This type of image printing apparatus includesa printer, a printing unit of a copy machine, and a printing unit of afacsimile. The above-mentioned organic EL panel can be applied tovarious types of image printing apparatuses. However, in the invention,two types of electrophotographic full color image printing apparatusesare used as examples of the image printing apparatus.

FIG. 7 is a longitudinal sectional view showing an example of an imageprinting apparatus using the above-described organic EL panels asline-type exposure heads. The image printing apparatus is a tandem-typefull-color image printing apparatus using a belt intermediate transfermethod. In the image printing apparatus, four exposure heads 10K, 10C,10M, and 10Y having the same configuration are arranged at exposurepositions of four corresponding photoconductor drums (image carriers)110K, 110C, 110M, and 110Y having the same configuration.

As shown in FIG. 7, the image printing apparatus is provided with adriving roller 121 and a driven roller 122, and an endless intermediatetransfer belt 120 is wound around these rollers 121 and 122 so as torotate around the rollers 121 and 122 in a direction indicated by arrow.Although not shown in FIG. 7, the image printing apparatus may beprovided with a tension applying member, such as a tension roller, thatapplies tension to the intermediate transfer belt 120.

The four photoconductor drums 110K, 110C, 110M, and 110Y each having aphotosensitive layer on its outer peripheral surface are arranged atpredetermined intervals from each other around the intermediate transferbelt 120. The suffixes K, C, M, and Y mean black, cyan, magenta, andyellow used for forming corresponding toner images, respectively. Thisis similarly applied to other members. The photoconductor drums 110K,110C, 110M, and 110Y are driven to rotate in synchronization with thedriving of the intermediate transfer belt 120.

A corona charging device 111 (K, C, M, and Y), the exposure head 10 (K,C, M, and Y), and a developing device 114 (K, C, M, and Y) are arrangedaround each photoconductor drum 110 (K, C, M, and Y). The coronacharging device 111 (K, C, M, and Y) uniformly charges the outerperipheral surface of the corresponding photoconductor drum 110 (K, C,M, and Y). The exposure head 10 (K, C7, M, and Y) writes anelectrostatic latent image on the charged outer peripheral surface ofthe photoconductor drum. The exposure heads 10 (K, C, M, or Y) arearranged such that a plurality of organic EL elements are aligned alongthe generatrix (main scanning direction) of each of the photoconductordrums 110 (K, C, M, or Y). The writing of an electrostatic latent imageis performed by illuminating light emitted from the plurality of organicEL elements onto the photoconductor drums with. The developing device114 (K, C, M, and Y) deposits toner, serving as a developing agent, onthe electrostatic latent image, thereby forming a toner image, i.e., avisible image on the corresponding photoconductor drum.

The black, cyan, magenta, and yellow toner images formed by the foursingle-color toner image forming stations are primarily transferred ontothe intermediate transfer belt 120 sequentially so as to be superposedonto one another on the intermediate transfer belt 120. As a result, afull-color toner image is obtained. Four primary transfer corotrons(transferring device) 112 (K, C, M, and Y) are arranged inside theintermediate transfer belt 120. The primary transfer corotrons 1112 (K,C, M, and Y) are arranged in the vicinities of the photoconductor drums110 (K, C, M, and Y), respectively, and electrostatically attract thetoner images from the photoconductor drums 110 (K, C, M, and Y) totransfer the toner images onto the intermediate transfer belt 120passing between the photoconductor drums and the primary transfercorotrons.

A sheet 102 as a target on which an image is to be finally formed is fedone by one from a sheet feed cassette 101 by a pickup roller 103, and isthen sent to a nip between the intermediate transfer belt 120 abuttingon the driving roller 121 and a secondary transfer roller 126. Thefull-color toner images on the intermediate transfer belt 120 aresecondarily transferred onto one side of the sheet 102 collectively bythe secondary transfer roller 126, and then the transferred image passesbetween a pair of fixing rollers 127, serving as a fixing unit, to befixed on the sheet 102. Thereafter, the sheet 102 is discharged to asheet discharge cassette that is formed on the top of the image printingapparatus, by a pair of sheet discharge rollers 128.

According to the above-described image printing apparatus, since theabove-mentioned organic EL panels are used as the exposure heads 10 (K,C, M and Y), it is possible to meet demands for a reduction in the sizeof the exposure head. In addition, since the quality of light emittedfrom the organic EL panel is hardly deteriorated, it is easy to keepdisplay quality for a long time.

FIG. 8 is a longitudinal sectional view showing another image printingapparatus using the above-mentioned EL panel as a line-type exposurehead. The image printing apparatus is a rotary-development-typefull-color image printing apparatus using a belt intermediate transfermethod.

In the image printing apparatus shown in FIG. 8, a corona chargingdevice 168, a rotary developing unit 161, an exposure head 167, and anintermediate transfer belt 169 are provided around a photoconductor drum(image carrier) 165.

The corona charging device 168 uniformly charges the outer peripheralsurface of the photoconductor drum 165. The exposure head 167 writes anelectrostatic latent image on the charged outer peripheral surface ofthe photosensitive drum 165. The exposure head 167, which is theabove-mentioned organic EL panel, is arranged such that a plurality oforganic EL elements are aligned along the generatrix (main scanningdirection) of the photoconductor drum 165. The writing of anelectrostatic latent image is performed by illuminating light emittedfrom the plurality of EL elements onto the photoconductor drum.

The developing unit 161 is a drum having four developing devices 163Y,163C, 163M, and 163K arranged at angular intervals of 90°, and isrotatable around a shaft 161a in the counterclockwise direction. Thedeveloping devices 163Y, 163C, 163M, and 163K respectively supplyyellow, cyan, magenta, and black toners to the photoconductor drum 165to deposit the toners as developing agents on an electrostatic latentimage, thereby forming a toner image, i.e., a visible image on thephotosensitive drum 165.

The endless intermediate transfer belt 169 is wound around a drivingroller 170a, a driven roller 170b, a primary transfer roller 166, and atension roller, and rotates around these rollers in a directionindicated by arrow. The primary transfer roller 166 electrostaticallyattracts the toner image from the photoconductor drum 165 and transfersthe toner image to the intermediate transfer belt 169 passing betweenthis photoconductor drum and the primary transfer roller 166.

More specifically, during the first one turn of the photoconductor drum165, an electrostatic latent image for a yellow (Y) image is written bythe exposure head 167, a toner image with the same color is formed bythe developing device 163Y, and the toner image is then transferred ontothe intermediate transfer belt 169. During the next turn of thephotoconductor drum, an electrostatic latent image for a cyan (C) imageis written by the exposure head 167, a toner image with the same coloris formed by the developing device 163C, and the toner image is thentransferred onto the intermediate transfer belt 169 so as to besuperposed on the yellow toner image. While the photoconductor drum 165makes four turns in this way, yellow, cyan, magenta, and black tonerimages are sequentially superposed on the intermediate transfer belt169. As a result, a full-color toner image is formed on the intermediatetransfer belt 169. When images are formed on both sides of a sheet onwhich the images are to be finally formed, a full-color toner image isformed on the intermediate transfer belt 169 in such a manner that tonerimages with the same color are transferred onto the front and rearsurfaces of the intermediate transfer belt 169, and then toner imageswith the next same color are transferred onto the front and rearsurfaces of the intermediate transfer belt 169.

A sheet conveying path 174 is formed in the image printing apparatus toallow a sheet to pass therethrough. A sheet is picked up one by one froma sheet feed cassette 178 by a pickup roller 179, is conveyed by aconveying roller along the sheet conveying path 174, and passes througha nip between the intermediate transfer belt 169 abutting on the drivingroller 170a and the secondary transfer roller 171. The secondarytransfer roller 171 electrostatically attracts a full-color toner imagecollectively from the intermediate transfer belt 169 to transfer thetoner image onto one surface of the sheet. The secondary transfer roller171 is adapted to approach and be separated from the intermediatetransfer belt 169 by a clutch (not shown). When a full-color image istransferred onto a sheet, the secondary transfer roller 171 is broughtinto contact with the intermediate transfer belt 169. When a toner imageis superposed on the intermediate transfer belt 169, the secondarytransfer roller 171 is separated from the intermediate transfer belt169.

The sheet having the toner image transferred thereonto in this manner isconveyed to the fixing unit 172, and then passes between a heatingroller 172a and a pressure roller 172b of the fixing unit 172, so thatthe toner image is fixed to the sheet. The sheet after the fixingprocess passes through a pair of sheet discharge rollers 176 to advancein a direction indicated by an arrow F. In a case of double-sidedprinting, after most of the sheet has passed between the pair of sheetdischarge rollers 176, the pair of sheet discharge rollers 176 arerotated in a reverse direction so that the sheet is introduced into aconveying path 175 for double-sided printing, as indicated by an arrowG. Then, the toner image is transferred onto the other surface of thesheet by the secondary transfer roller 171 and the fixing unit 172performs the fixing process on the toner image again. Then, the sheet isdischarged by the pair of sheet discharge rollers 176.

Since the above-mentioned image printing apparatus uses theabove-mentioned organic EL panel as the exposure head 167, it ispossible to meet demands for a reduction in the size of the exposurehead. In addition, since the quality of light emitted from the organicEL panel is hardly deteriorated, it is easy to keep display quality fora long time.

Although the image printing apparatus has been described as an exampleof the electronic apparatus including the organic EL device according tothe invention, the organic EL device according to the invention can alsobe applied to other electrophotographic image printing apparatuses, suchas an image printing apparatus that directly transfers a toner imageonto a sheet from a photoconductor drum without using an intermediatetransfer belt, an image printing apparatus that forms a monochromaticimage, and an image printing apparatus that uses a photoconductor beltas an image carrier.

1. A light-emitting device, comprising: a substrate; an insulating layerformed of an inorganic compound and having an upper surface, theinsulating layer formed on the substrate; a plurality of light-emittingelements formed in a region over the insulating layer, each of thelight-emitting elements having an anode, a thin organic light-emittinglayer, and a cathode sequentially stacked above the insulating layer,the cathode of at least one of the light emitting elements having anupper surface defining a step, the light-emitting elements emittinglight by excitation due to an electric field; an insulating pixelpartition wall separating the anodes of at least two of thelight-emitting elements; an organic buffer layer having outer and innersurfaces, the organic buffer layer being formed of an organic compoundand covering an area that is larger than the region in which thelight-emitting elements are formed, the inner surface of the organicbuffer layer filling the step of the upper surface of the cathode suchthat the outer surface of the organic buffer layer is substantiallyflat; and first and second gas barrier layers, formed of an inorganiccompound, disposed on the outer surface of the organic buffer layer, andshielding the plurality of light-emitting elements from an environmentexternal to the device, only one of the first and second gas barrierlayers covering an area larger than the organic buffer layer.
 2. Thelight-emitting device according to claim 1, further comprising: acathode protection layer that is provided between the cathode and theorganic buffer layer and is formed of an inorganic compound.
 3. Thelight-emitting device according to claim 1, the first gas barrier layercovering an area larger than the organic buffer layer, and the secondgas barrier layer covering an area that is smaller than the organicbuffer layer and larger than the region where the light-emittingelements are formed.
 4. The light-emitting device according to claim 1,the second gas barrier layer being thicker than the first gas barrierlayer.
 5. An electronic apparatus, comprising: the light-emitting deviceaccording to claim
 1. 6. A light-emitting device, comprising: asubstrate; an insulating layer on the substrate; a plurality oflight-emitting elements formed in a region over the substrate, each ofthe light-emitting elements having an anode, a thin organiclight-emitting layer, and a cathode sequentially stacked above theinsulating layer, the cathode of at least one of the light-emittingelements having an upper surface defining a step, the light-emittingelements emitting light by excitation due to an electric field; aninsulating pixel partition wall separating the anodes of at least two ofthe of light-emitting elements; an organic buffer layer having outer andinner surfaces, the organic buffer layer being formed of an organiccompound and covering an area that is larger than the region in whichthe light-emitting elements are formed, the inner surface of the organicbuffer layer filling the step of the upper surface of the cathode suchthat the outer surface of the organic buffer layer is substantiallyflat, the organic buffer layer having end portions; and a gas barrierlayer formed of an inorganic compound and covering the organic bufferlayer in order to protect the plurality of light-emitting elements froman environment external to the device, the gas barrier layer having afirst portion and a peripheral portion, the first portion covering theregion where the plurality of light-emitting elements are formed andbeing thicker than the peripheral portion, the peripheral portioncovering the end portions of the organic buffer layer.
 7. Thelight-emitting device according to claim 6, wherein the insulating layerhas an upper surface, the light-emitting device further comprising: inthe end portions of the organic buffer layer, an angle between the outersurface of the organic buffer layer and the upper surface of theinsulating layer on the substrate being 20° or less, the insulatinglayer being formed of an inorganic compound.
 8. A light-emitting device,comprising: a substrate having a light-emitting region; a light-emittingelement disposed above the substrate in the light-emitting region, thelight-emitting element having a first electrode, a second electrode, anda light-emitting layer disposed between the first electrode and thesecond electrode; an organic buffer layer disposed over thelight-emitting element and being formed of an organic compound, a regionof forming of the organic buffer layer being larger than thelight-emitting region; a first gas barrier layer disposed over theorganic buffer layer and being formed of an inorganic compound, a regionof forming of the first gas barrier layer being larger than the regionof forming of the organic buffer layer; and a second gas barrier layerdisposed on the first gas barrier layer and formed of an inorganiccompound, a region of forming of the second gas barrier layer beingsmaller than the region of forming of the organic buffer layer.
 9. Alight-emitting device, comprising: a substrate having a light-emittingregion; a light-emitting element disposed above the substrate in thelight-emitting region, the light-emitting element having a firstelectrode, a second electrode, and a light-emitting layer disposedbetween the first electrode and the second electrode; an organic bufferlayer disposed over the light-emitting element and being formed of anorganic compound, a region of forming of the organic buffer layer beinglarger than the light-emitting region; and a gas barrier layer disposedover the organic buffer layer and being formed of an inorganic compound,a region of forming of the gas barrier layer being larger than theregion of forming of the organic buffer layer, the gas barrier layerhaving a first portion covering the light-emitting region and a secondportion covering an edge portion of the organic buffer layer, thethickness of the first portion is larger than the thickness of thesecond portion.